Oculomotor behavior as an "ideal system" for the study of the neurophysiologic mechanisms of voluntary and reflex behavior. As an overt and measurable behavior, motor systems are ideal for study of the fundamental mechanisms for how the brain transforms sensory inputs and volitional commands into outputs. Among the motor systems, eye movements have the advantage of being relatively simple. In order to study volitional behavior in vivo, we use chronic recording techniques in trained primates. In one set of experiments, we are studying the fundamental cellular and circuit mechanism for generating saccadic eye movements, the high-velocity eye flicks that one uses to scan the surrounding environment. The brain circuit that generates saccadic behavior is essentially a biologic machine that acts like a central pattern generator, a closed-loop neural circuit that creates a stereotyped motor output in response to inputs from higher centers. Like any machine, one can attempt to understand how it works by "reverse engineering." That is, given the machine's output, how do the internal circuits function to produce that output? One systems engineering approach is to inject characteristic input signals at critical points within the circuit and compare the output to quantitative predictions based on assumptions about the biological mechanisms. Using this approach, we have addressed several fundamental issues in oculomotor physiology, which in turn reveals brain mechanisms that are general to all behavior. By studying the brain in live and behaving subjects, we obtain fundamental insight into how it computes, plans movements and represents information. We come to understand the brain's wiring diagrams and how networks of interconnected neurons function together as an effective biologic machine. Such basic biology research is essential as the fundamental underpinning for understanding brain function when compromised by disease or injury. The health relatedness of this research is that the understanding of how the normal, healthy brain works is a sine qua non for understanding the human condition in health and in illness.